In order to diagnose and cure central visual losses (e.g., in a patient who is unable to properly perceive visual motion) we must first gain an understanding of the neural processing in visual cortex. The long-term goal of this research is to develop a detailed, quantitative, predictive model of cell function in primary visual cortex. We will have succeeded when/if we can record from a cell while presenting a fixed set of visual stimuli (to measure model parameters), and then be able to predict the cell's response to any visual stimulus. The computational/theoretical research proposed in this application is designed to complement empirical research by clarifying the interpretation of experimental results and by making a number of empirically testable predictions thereby suggesting new experiments. Specifically, we aim to: (1) Reconcile the controversy regarding the origin of selectivity of simple and complex cells; (2) Reconcile the controversy over the role of intracortical (e.g., cross-orientation) suppression; (3) Explain the variability, from cell to cell, of contrast-response data.